2013 04 08 modifying the plotter
I took the tool holder that I made on 2013-03-20 and inserted a nail into the end to try to make a holographic scratch.This was a useful excercise, but not actually very successful. The tip wasn't sharp enough to draw well with the relatively light pressure that the plotter applies. Using a sharper tip helped, but it tended to skip across the plastic rather than drawing a smooth line. Here's what the mount looked like with a small nail installed:
Next, I decided to try a vinyl cutter, like the one that Ilan let me use with the CNC mill before. I bought this from eBay: 11.5mm Blade Holder for Roland Cutting Plotter Cutter + 3 pcs 45° Blade Knife
And it actually fits in the plotter! I did need to tie it in place to hold it more securely.
The cutter works, but it seems to make its scratches slightly too deep. They're not quite as brilliant as the ones I can make by hand. I'm experimenting with removing the spring that presses the pen down when it's lowered so that I can replace it with an adjustable weight.
Here's an example of the difference between the vinyl cutter on the plotter and my own tools.
This picture shows two scratches. The top one is from the vinyl cutter in the plotter, and the bottom one is from my preferred compass which I controlled by hand:
The light source was a single white LED about 30cm away, and both scratches had a radius of about 2cm. Note how the reflection from the lower scratch is brighter and more concentrated (I think this is what I mean when I say that a scratch is more "brilliant" or "clear").